Just using a voltmeter or plug-in tester won't detect every wiring fault, although I also recommend getting a plug-in outlet tester to verify the outlets around your house, or if you are a camper, to check every power pole (along with the NCVT) every time. The advantage of using the NCVT is it will detect a wiring condition that the plug-in testers won't, which Jim Sokol has discovered as a potential problem and he discusses in the articles I link to below. Jim has spent thousands of hours and his own dime to promote this issue in the RV community where it is more likely to occur and more likely to be deadly when it does.

Personally I've been promoting it on the RV sites I run and visit after an experience I had a year ago. Within days of posting this info elsewhere I've had people respond that they bought a NCVT and immediately detected a problem. Last summer I moved our camper to our backyard so I could clean the roof and the A/C coils. I had my kids get in their bathing suits to wash the camper, water went everywhere, the ground was soaked, and they had some summer fun while they worked. Long after they were done, I had to get into the camper, so I did what RVers have done hundreds of times - I grabbed the door handle while I stood on the wet ground. I received a noticeable shock, and with my background I immediately knew something wasn't wired right. Worse, I knew that the entire time my kids were washing our camper they could have been killed. They were far more conductive than I was; I was wearing rubber-soled shoes and my hand was dry, they were soaked all over, deep into their skin, and were in bare feet. I don't know how, but only by extreme luck did a nice summer day in the backyard not turn into an awful day at the morgue. I tracked my problem down to a bent ground pin on my 30 amp RV extension cord.

Everyone here is more electric-savy than your average RVer, and ground problems are probably less common on PV systems than for RVs (due to bad wiring at power poles and lots of vibration on the road). I was lucky and just got a warning, but it could have been an electrocution. Slightly different conditions and you are dead. Saltier water (think beach environments) is more conductive, slightly higher voltage on a given day, or you get the shock through both arms and not both legs (amps through your heart is what usually kills you). My shock was across my heart (1 arm and 2 legs) so I was just as lucky that day as my kids. I'm sure because the measured voltage on that fault was only around 60 volts and not the full 120, and there wasn't any equipment fault providing full amperage to the chassis, just normal equipment leakage and a bad ground. That probably saved all of us.

Check out these links, especially the article at the first link, which explains the right way to test for ground issues. The 2nd link explains how voltmeters, plug- in testers, and intelligent surge protectors can report on some faults - but not all. Some of this is geared towards the RV crowd but it applies just as much to the PV crowd since so many of you are do-it-yourselfers and are working around live equipment.

Edit: There is some confusion that this does not apply to the DC components in a PV system, but this is not true. While the NCVT will not detect a dangerous DC voltage, all of the components in the system are connected via the ground wiring. If any AC component in the system has an equipment fault that energizes the case, and the connection to the physical ground has failed, that AC voltage will exist on all cases/frames. So you do need to check the frame of your PV panel even though it is a DC component.

Attachment not found.
And these usually need two good AA Batteries and have a specific range of voltages/frequencies that this work with:

Frequency Range: 50-500 Hz

Batteries: Two alkaline 1.5V AAA

Voltage Range: 50-1000 Volts AC

They will not work with any DC voltage (i.e., will not detect a "hot" 48 VDC battery bus).

Also, "tip" of the tool needs to be close to the metal surface or plastic insulation of the wire/RV chassis/etc. being tested.

And there are some issues with how they work that you need to be aware of. There are sometimes when they will indicate a "hot surface/wire" but you may not get a shock or have a short circuit. Many pieces of electronics use capacitors to filter radio interference on the input AC power lines. If you have a floating ground, these capacitors can energize the RV chassis with 60 to 120 VAC relative to ground, but you will only have (in theory according to safety code) a maximum of 2.5 milliamps of current (and frequently 60 VAC). It is not usually enough to kill you, but it can give you a "bite" (and probably will not trip a GFI outlet). Fixing the ground path (like Teckntrek did) will fix the floating ground problem.

Also--This may give false "no voltage present" or weak indications when measuring cables with Hot and Return bound together (like extension cords). The tester works by acting like one half of a capacitor to pick up AC electric fields near the hot wires. If you have a return wire right next to the hot wire, it can cancel most of the electric field and look "dead" to the NCVT. If you are going to work on an extension cord/ROMEX cable, etc. (change an outlet, etc.), check with the tester on each wire or at the outlets themselves (push the tip of the NCVT into the outlet slot).

I agree that these are very handy tools to have around. I had my sister get one a few months ago--She just bought a house and wanted to learn how to do basic electric work. The NCVT makes it much easier to verify if an AC (alternating current) circuit is safe to work on or not (verify that the circuit was hot, but now cold when the correct breaker was turned off).

The NCVT I linked to in my first post is one that Jim has tested and gives a reading at a low enough voltage (around 40) to give a warning before it gets into a lethal range (amperage kills you, but higher voltage makes it easier to complete the path). He posted the following on another forum about using other brands:

As far as NCVT (Non Contact Voltage Testers) there are a few alternatives to the Fluke tester shown in my article that are a little less expensive and more available at Home Depot or Lowes. For instance, the Klein NCVT-1 has similar sensitivity to the Fluke VoltAlert and is perhaps $10 cheaper. Klein also makes a dual-range NCVT-2 that will test for really low voltages as well, but it may be a little too complicated for a casual user. So please shoot me a message if you're looking at any other brands before you buy them. I try out all my test gear on a calibrated voltage/distance tester, and not all Voltage testers work exactly the same. I know the Fluke VoltAlert works great, and the Klein NCVT-1 works just as well. And I have a handful of others that also work. But it's best not to go cheap on test gear, especially when lives are at stake.

Sounds like a neutral/ground bonding issue in the RV breaker box. Some neutral return current was traveling on the EGC back to source. As you removed power by opening breakers the current on the EGC reduced in step. Just guessing of course.

Update the thread title and I believe Marc/Cariboocoot maed this a sticky.

-Bill

Thanks for doing that since I was a bit confused and in disagreement with the original post. A bit too "Chicken Little" IMHO. As you pointed out, those voltage detectors are of no use for DC voltages and unless one has microinverters, almost all electrical work (and associated dangers) on a PV system involves DC.

That said - no one should be mucking around with a PV system unless they understand the basic principles of working with DC electricity and the dangers involved.

Sounds like a neutral/ground bonding issue in the RV breaker box. Some neutral return current was traveling on the EGC back to source. As you removed power by opening breakers the current on the EGC reduced in step. Just guessing of course.

No bonding on RVs. They depend on the bond at the campground. Otherwise there would be 2 bonds, against code.

Which is a problem when you use a generator, since most smaller generators that would be used with RVs don't provide a N-G bond. Personally I created a plug that I leave in one of my genset's outlets which does nothing but create a N-G bond, per a recommendation from Jim.

Thanks for doing that since I was a bit confused and in disagreement with the original post. A bit too "Chicken Little" IMHO. As you pointed out, those voltage detectors are of no use for DC voltages and unless one has microinverters, almost all electrical work (and associated dangers) on a PV system involves DC.

That said - no one should be mucking around with a PV system unless they understand the basic principles of working with DC electricity and the dangers involved.

Hardly chicken little. An energized case/frame can kill you, period. This isn't a minor warning like "don't discharge your battery more than 50% SOC", or a code issue like "make sure each string has its own fuse". Plus, how is the original title of "Important - check this every time you work on your solar system" chicken little at all?

No bonding on RVs. They depend on the bond at the campground. Otherwise there would be 2 bonds, against code.

Which is a problem when you use a generator, since most smaller generators that would be used with RVs don't provide a N-G bond. Personally I created a plug that I leave in one of my genset's outlets which does nothing but create a N-G bond, per a recommendation from Jim.

OK, it sounds like you are satisfied that no greater problem exists than "normal equipment leakage". Everyone's definition of safe is different. If there was enough current to shock me to earth from the chassis and all I did to correct the problem was to straighten a bent grounding pin, that would not fit my definition of safe.

Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

techtrek - I appreciate your concern for safety and I do think that safely working wtih any electrical equipment requires some knowledge and a lot of common sense. Please don't take my criticisms of your post personally.

Well maybe. It really depends on the energy present in the voltage (or current) source and a bunch of other factors - skin/body resistance, capacitance, etc. For example - you can get quite a shock form thousands of volts with electrostatic discharge and never be in any danger because there is little energy present. The same can be true of a shock from the case of any electric equipment or appliance depending on what is responsible for for the potential difference present.

The resistance of human skin/body means that it is very difficult (almost impossible) for 12V, 24V or even 48 V DC to to kill you.

Test: take your multimeter and hold each probe tightly between the fingers of both hands to measure the resistance across the your body and through your heart (which is the path which requires the least energy to kill you).

Now, divide 12 Volts (or 24, or 48V) by that number to get the current that could potentially pass through your heart. '

Yes, wet skin can reduce the resistance (and increase current) but by how much? Easy to do this experiment yourself.

For DC current, it takes a minimum of approximately 300 milliamps to kill a person.....

For AC current the situation is different. Human skin has some capacitance and it take less AC current passing through the heart to kill (minimum 30 millamps or so) so AC is more dangerous in that way - but still requires fairly high voltages...

Lots of damage can occur from both DC and AC voltages and current that are less than lethal levels - particulalry if sustained for long periods- tissue burns, etc - but it fortunately is really pretty difficult to kill some one with electricity - at least with the low voltages present in most PV systems.

The biggest issue I have with the OP is that it seems to focus on using a non contact voltage detector to ensure safety when working on a PV system. The problem, as I stated before, is that there is very little AC equipment in most PV systems and as Bill pointed out NCV detectors are useless at detecting DV voltage.

I've spent many hours installing and working on my PV system and almost never have I worked on the AC side. I do own a NCV detector but that is for use when working on my home AC wiring - a different thing all together.

IMO - you face more danger from an energized case on an improperly grounded household AC appliance - especially if your home has older wiring without GFCIs. But no one is running around saying "Danger, don't use your toaster without first using a NCV detector"

Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

Wow. I'm just amazed I'm not dead already.

Look boys and girls: when we're talking about improper electrical wiring or something gone wrong you can not know in advance what the Voltage or current potential is. This is because you probably don't even know if something is wrong until you touch it and get the tingle. Hopefully all you will get is a tingle, but if not it can be too late in an instant - and so will you.

With an RV there usually is no actual Earth ground so in essence it is never safe. A grounding strap or plate may help, but nothing is ever 100% certain.

I use a NCVD myself because I'm too often working on something someone else installed/modified/botched completely. I always expect the wiring to be wrong unless I did it.

Yes it can be a matter of life or death and it's interesting that mtdoc after decrying the claim goes ahead and shows how little it can take.

Don't be paranoid, but be cautious.

And if there's any more ungracious behaviour I shall hack this thread to bits.

Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

Coot'

I'm not sure what you mean by "ungracious behaviour' - please explain. If anything I said offended someone personally, I apologize. I hope that disagreeing with someones post is not considered ungracious...

Yes, it takes relatively little current passing through the heart to kill someone but it takes A LOT of energy and high voltage to allow that much current to past through the human body - more than present at most points in a PV system.

Again - I'm not denying that there are dangers anytime one works with electricity and that safety precautions and common sense are not needed. I'm just disagreeing with the idea that one is risking their life working on a PV system if they aren't using a NCV detector to check every piece of (mostly DC) equipment they touch.

Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

I don't think anyone was suggesting you use an NCVD for DC especially as it won't work. It is AC you are more likely to come in contact with at dangerous levels (except for GT systems where the 300+ VDC can turn you into a corpse pretty quickly). Nor would one have necessarily shown the energized frame of the RV encountered.

I've been whacked by a lot of electrical shocks in my life, some of them very high Voltage. And I've known people who were paranoid about 12 Volt car batteries - even after I wet two fingers and touch both terminals to show them how safe it is. So far I'm not dead, but the first time can always be the last time so the point is well-taken that electricity can be deadly. Especially when you don't know it's there.

I don't think anyone was suggesting you use an NCVD for DC especially as it won't work. It is AC you are more likely to come in contact with at dangerous levels (except for GT systems where the 300+ VDC can turn you into a corpse pretty quickly). Nor would one have necessarily shown the energized frame of the RV encountered.

I think there's a good chance to come into contact with dangerous levels of DC in a system with a DC GFP. If the GFP is tripped you might find your DC negative wiring at string voltage above ground. It takes a lot less than 300+ volts to give me a once in a lifetime tingle.

For folks with DC lighting in the house... those lamp sockets in the kitchen and bathroom could be real killers.

I think there's a good chance to come into contact with dangerous levels of DC in a system with a DC GFP. If the GFP is tripped you might find your DC negative wiring at string voltage above ground. It takes a lot less than 300+ volts to give me a once in a lifetime tingle.

For folks with DC lighting in the house... those lamp sockets in the kitchen and bathroom could be real killers.

--vtMaps

And what is "string Voltage"? Undefined variable.
NEC considers Voltages over 60 as "high" so a battery-based system array may or may not be high Voltage.
Not all systems have DC GFCI (thank goodness) and I am well aware of its failings as outlined by our own B.B. Bill.

Re: Important - check AC Wiring/Voltage Safety every time you work on your solar system

One reason I am not a huge fan of using NCVD for "safety" reviews is that they don't always work as people expect...

Besides the issues of non-DC alerts and issues of Hot/Return wires next to each other giving weak indication of dangerous AC voltages present...

There is using the NCVD for sensing "hot grounds" (60 VAC or higher) in an arbitrary environment.

The NCVD uses your body as the other side of a capacitor (the tip is the input side). For most situations, that works pretty well. Your body is pretty much coupled to earth ground and any sensed AC voltage will be relative to your body--Or earth ground.

If you are concerned that your RV is "Safe" (possible broken plug, miss-wired campground AC power outlet, etc.)--You can use your NCVD when you are standing outside the RV (at arm's length) and hold the tip next to the RV body--That could indicate if the RV chassis is "hot".

If you did the same test when you are standing inside the RV, the NCVD will indicate that there is no problem with a "hot ground"--Because your body is now referenced to the RV chassis surrounding you.

A good tool for checking unknown electrical connections is still the AC outlet tester (like Marc/Cariboocoot usually suggests). It will indicate most of the common loss of power, ground/reversed hot/neutral connections, and such.

Good points and I agree about the dangers of DC GFPs (and why I disabled mine by bonding my bat neg to ground).

You do have to keep in mind that PV strings are current sources (not voltage sources) so the voltage will drop dramatically depending on the applied load. The MegaOhms of resistance from skin to ground or skin to skin present quite a load!

I appreciate all of Bill's points about NCV detectors. I would not want someone reading this thread and going around with their newly purchased NCV detector - testing parts of their PV system and thinking there is no danger of shock because their new tool tells them it's safe....:roll:

You do have to keep in mind that PV strings are current sources (not voltage sources) so the voltage will drop dramatically depending on the applied load. The MegaOhms of resistance from skin to ground or skin to skin present quite a load!

I'm confused again. High resistance equals low load (i.e. current) that last time I looked. In order to overcome such high resistance you need high Voltage. That's why even though a 12 Volt battery has a huge current potential it's safe to touch the terminals because the low Voltage can not overcome the high resistance of your body.

BTW I've had the NCVD give false readings on 120 VAC circuits before; in both directions. So even when you're safe you may not be safe. But there's only so much you can do to protect yourself. At some point you'd end up with so many safety precautions it is impossible to do the job.

OK, it sounds like you are satisfied that no greater problem exists than "normal equipment leakage". Everyone's definition of safe is different. If there was enough current to shock me to earth from the chassis and all I did to correct the problem was to straighten a bent grounding pin, that would not fit my definition of safe.

Well maybe. It really depends on the energy present in the voltage (or current) source ...

I did use the word "can" and not "will".

and a bunch of other factors - skin/body resistance, capacitance, etc. For example - you can get quite a shock form thousands of volts with electrostatic discharge and never be in any danger because there is little energy present. The same can be true of a shock from the case of any electric equipment or appliance depending on what is responsible for for the potential difference present.

Yup. Lots of factors on whether you are killed or not, including voltage and amperage present, and environmental conditions. I covered that.

The resistance of human skin/body means that it is very difficult (almost impossible) for 12V, 24V or even 48 V DC to to kill you.

Yes, which is why my post was about 40+ volts AC.

Test: take your multimeter and hold each probe tightly between the fingers of both hands to measure the resistance across the your body and through your heart (which is the path which requires the least energy to kill you).

I covered the body pathing issue, yes.

......really pretty difficult to kill some one with electricity - at least with the low voltages present in most PV systems.

The biggest issue I have with the OP is that it seems to focus on using a non contact voltage detector to ensure safety when working on a PV system. The problem, as I stated before, is that there is very little AC equipment in most PV systems and as Bill pointed out NCV detectors are useless at detecting DV voltage.

It doesn't matter how much AC equipment is in a PV system, one single fault of that AC equipment, or any AC equipment, if there is also a ground fault, will mean ALL of the equipment frames that are all grounded together will have live cases. This is a critical point.

An example Jim gives in his articles is - an equipment fault in another RV on the same subpanel as your RV, assuming the subpanel has a missing ground, means YOUR RV is now also energized.

I've spent many hours installing and working on my PV system and almost never have I worked on the AC side. I do own a NCV detector but that is for use when working on my home AC wiring - a different thing all together.

Incorrect. See my item in bold above. You need to check everything. Equipment failure + bad ground, and now your PV frame is live with AC voltage.

Look boys and girls: when we're talking about improper electrical wiring or something gone wrong you can not know in advance what the Voltage or current potential is. This is because you probably don't even know if something is wrong until you touch it and get the tingle. Hopefully all you will get is a tingle, but if not it can be too late in an instant - and so will you.

That is where the NCVT comes in, test first and you'll know something is wrong before you get that tingle.

With an RV there usually is no actual Earth ground so in essence it is never safe. A grounding strap or plate may help, but nothing is ever 100% certain.

Yes there is, it is provided by the campground's subpanel. If you are using a generator, you have a floating ground and therefore there is no possible path to the physical ground so no danger exists there (instead the ground either doesn't exist at all or if you create N-G bond, the possible path is to the camper frame).

...
If you are concerned that your RV is "Safe" (possible broken plug, miss-wired campground AC power outlet, etc.)--You can use your NCVD when you are standing outside the RV (at arm's length) and hold the tip next to the RV body--That could indicate if the RV chassis is "hot".

If you did the same test when you are standing inside the RV, the NCVD will indicate that there is no problem with a "hot ground"--Because your body is now referenced to the RV chassis surrounding you.

...

Yes, standing outside with a firm grip on the NCVT is the proper test when connected to a campground. If you are connected to a generator the proper test is to stand inside the RV since the ground is the camper chassis.

It doesn't matter how much AC equipment is in a PV system, one single fault of that AC equipment, or any AC equipment, if there is also a ground fault, will mean ALL of the equipment frames that are all grounded together will have live cases. This is a critical point.

An example Jim gives in his articles is - an equipment fault in another RV on the same subpanel as your RV, assuming the subpanel has a missing ground, means YOUR RV is now also energized.

Incorrect. See my item in bold above. You need to check everything. Equipment failure + bad ground, and now your PV frame is live with AC voltage.

OK. Please explain how a fault in a home PV system - will cause my PV panels, PV wire run, charge controller, or any DC wiring or enclosure to become energized with AC.